Using Laser Light to Excite Helium Atoms
to High Energy States
James Dragan, Yuan Sun, Harold Metcalf,
Stony Brook University, Stony Brook NY 11794-3800
Bohr Atom
STIRAP
Helium Energy Levels
n = 4 Rydberg State
Simplified
Diagram
792-­‐830nm STIRAP Beams [1]
intuiGve order counter-­‐intuiGve order Gme Gme 3 Stimulated Adiabatic
Rapid Passage utilizes the
counter-intuitive order to
populate the third state
Excitation by
discharge
This is a diagram of Hydrogen as described by Neils Bohr in 1913. Note 2
the increasing radial distance of each orbital as r ! n
2 1 [3]
The Experimental Setup Detection Systems
Vacuum System
Atomic Physics
In 1888 Rydberg created a generalized version of Balmer’s simple empirical
formula for the wavelengths of the H atom. This is impressive because the
structure of an atom was still being debated at this time.
We can then further expand our understanding of atoms by at Bohr’s 1913 solar
system-like picture to describe the Hydrogen Atom. This model corroborates
the Rydberg formula and gives a basic picture to the structure of an atom.
[3]
Rydberg Atoms
[3]
A Rydberg atom is an excited atom with one or more electrons in a very high
orbital n. The name is usually used when n > 15. Because of its large physical
separation from the nucleus, the outer electron experiences a very weak
attractive force from the nucleus and is therefore quite weakly bound to it.
Source Chamber
LN2 cooled
He* beam
Avg.
Longitudinal
Velocity
1070m/s
Full-Width at
Half-Max
480m/s
Stainless Steel Detector- The SSD uses two
Ion Detector-For Rydberg atom
MCP’s allowing us to detect electrons from the
detection. Uses two microchannel plates
He*. A He* atom ejects an electron which
(MCP) which amplify the original
results in a cascade of electrons from the MCP.
signal, gain is related to the electric field
We are able to move it perpendicular to the
and geometry of MCP.
atomic beam giving us quantitative
measurements on the atomic distribution.
Past Efficiency Measurements
Interaction Chamber
STIRAP
Lasers
Source STIRAP v
2.3 kV [4]
STIRAP, Stimulated Rapid Adiabatic Passage, is used in our experiments to
excite atoms to Rydberg states with n=15-50. The theory of STIRAP describes
how it can achieve 100% population transfer. This is possible because we
effectively do not populate the intermediate state of the system if we use the
counter-intuitive order. The counter-intuitive order means that the laser light
associated with the 2 to 3 state transition interacts with the atomic beam before
the light associated with the 1 to 2 transition. We excite an atomic beam of
metastable state Helium (He*) to Rydberg states by exploiting an intermediary
state.
Figures from posters by :
[1] Xiaoxu Lu et al., Bull. Am. Phys. Soc. 55, No. 5, 119341 (2010) K1 00089
[2] Xiaoxu Lu et al., Bull. Am. Phys. Soc. 56, No. 5, 152 (2011) Q1 14.
[3] X. Lu, Ph.D. thesis, Stony Brook University, 2011
[4] Petr Anisimov et al., Bull. Am. Phys. Soc. 57, No. 5, 99 (2012) K1 19.
These measurements show
the efficiency of Rydberg
Atom production as the
He* passes through the
STIRAP light beams. This
is done by deflecting all the
unexcited He* atoms using
a laser of wavelength
1083 nm, after they pass
through the STIRAP beam.
[3]
URECA Celebration of Undergraduate Research and Creativity, April 24th • Stony Brook, NY
389 nm Due to these interesting properties, creating and studying Rydberg atoms has
been the focus of many research projects in the past several decades.
796 nm These Rydberg atoms have several interesting properties.
•  Exaggerated response to external electric and magnetic fields
•  Under some conditions, the electron in the high n orbital behaves like a
classical electron orbiting a nucleus
•  Because of its huge size, r ! n 2 ,the electron in the high energy state is
actually quite fragile. This means we can remove it from its orbital by
applying a voltage difference. This is how we measure how many Rydberg
Atoms we have.
•  Long lifetime
[3]
Detector Tekhnoscan
Ti:Sapphire
Tunable from
690-1100nm
"Red Light"
Schwartz
Electro-Optics
Ti:Sapphire;
frequency
doubled by
Coherent Model
MBD 200
778nm;
frequency
doubled to
389nm
"Blue Light"
[1]
Theory suggests that we should be able to achieve 100% population transfer to the
Rydberg state. Experimental results have only achieved ~50% population transfer.
We believe this is due to the transverse velocity spread of atoms that results Doppler
Shifting them out of resonance. Recent experiments have been conducted using
optical molasses to decrease this velocity spread.
Work is supported by the Office of Naval Research.